Large cargo containers and the like having enclosed bodies are conventionally provided with a rectangular door frame at one end of the container. A pair of doors, which are adapted to be swung within the plane of the door frame, are typically provided for closing the door frame. A rotary bar locking mechanism selectively retains the doors within the door frame. The doors on the container are constructed as large as possible to facilitate loading and unloading of the container.
The size of many cargo containers is substantially regulated by Industry standards. That is, Industry standards regulate the height of the container as measured from a road bed and the width of the container. Standard sized wheel trucks govern the distance between the road bed and a base of the cargo container.
In that the outside measurements of the container are substantially regulated by Industry standards, the container is typically fabricated from relatively thin materials to maximize internal cargo space, transport capability, and for purposes of economy. The door frame of the container comprises top and bottom transverse frame members including an upper header and a lower sill and vertical side members. The frame members are suitably welded at their adjacent corners.
To promote loading and unloading of the cargo container and to maximize interior cargo space, the door frame is usually fabricated of structural members having the least strength practical. To further facilitate the loading and unloading of the container, the top transverse frame member or header should be fabricated as narrow as possible so as to not hinder loading and unloading of the cargo container.
Because of its relatively large size and the weakness of its structural members, under certain circumstances, such as when a racking action is applied to the container, the door frame is subject to considerable distortion. When a racking action is applied to the container, the header moves, or tends to move, relative to the sill in a path that is transverse to the length of the cargo container and generally parallel to the sill. Such racking action tends to occur if the vehicle is not standing in a level position so that its rear wheels are on different levels; it also tends to occur from twisting or jostling of the body during travel, particularly at high speeds.
It is common practice to utilize the doors, when closed, to stiffen the frame of the cargo container. The rotary bar locking mechanism associated with each door on the cargo container is used to align the respective door relative to the door frame and retain the doors in a closed position within the door frame thereby adding stiffness to the cargo container frame.
Each rotary bar locking mechanism typically includes a shaft rotatably attached on the exterior side of each door and extends parallel to the pivot axis of the door along or adjacent to the door's free end. A handle is fixed to the shaft to facilitate rotation thereof. A latch is typically provided at opposite ends of the shaft. Each latch is adapted to coact with a keeper secured to the respective header and sill of the door frame. Each latch is typically provided with an elongated and tapering cam finger which coacts with a respective keeper to provide a useful mechanical advantage to close the door even though the door frame may be twisted because the vehicle is parked on uneven terrain.
An elastomeric frost seal is commonly used to form an air tight closure between the doors and the frame. When the truck has two adjacent pivot doors, a frost seal is also fixed to the free end of one of the doors and forms and air tight seal between the doors.
The rotary bar locking mechanism must be effective to release the doors in minimum time and with minimum difficulty even under severe and abnormal conditions. Such severe and abnormal conditions arise in service due to factors such as distortion or sagging of one of the doors or the presence of ice, dirt and the like in the bar locking mechanism.